Automatic external defibrillator with active status indicator

ABSTRACT

An AED includes defibrillation circuitry housed within an enclosure, a first processor programmed to periodically test the operability of the defibrillation circuitry and a second processor in communication with the first processor. The AED further includes a visual indicator, such as a red/green LED, positioned at the exterior of the enclosure that is operatively connected to the second processor. The second processor is programmed to control the visual indicator in response to the periodic test results provided to it by the first processor.

RELATED APPLICATIONS

This is a continuation-in-part of application Ser. No. 10/453,312, filedJun. 3, 2003 now U.S. Pat. No. 7,495,413 which is a continuation ofapplication Ser. No. 09/960,859, filed Sep. 21, 2001 now U.S. Pat. No.6,577,102.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to external defibrillators, and morespecifically to automatic external defibrillators (AED) having activestatus indicators that provide a continuous indication related to theoperational readiness of the defibrillator. The invention furtherrelates to AEDs having other operation indicators that provideindications related to the condition of the defibrillator during use.

2. Description of Related Art

Conventional AEDs perform periodic self-tests to determine theoperational readiness of the defibrillator. Some defibrillators performsuch self-tests automatically when they are turned on. Otherdefibrillators perform self-tests on a periodic basis regardless of theon/off state of the defibrillator. The results of these tests, however,may not be indicated until subsequent turn-on of the AED or may not bereadily apparent to the user of the AED.

Hence, those skilled in the art have recognized a need for providing acontinuous, active indication of the operational readiness of anexternal defibrillator regardless of the on/off state of thedefibrillator. The need for additional indications of the condition of adefibrillator during use has also been recognized. The inventionfulfills these needs and others.

SUMMARY OF THE INVENTION

Briefly, and in general terms, the invention is directed to an AED thatprovides a continuous, active indication of the operational readiness ofthe defibrillator. This active indication is provided by a visualindicator carried by the enclosure of the AED. The visual indicator maybe a single LED capable of displaying different first and second colors,e.g., red and green. Alternatively the visual indicator may be twoseparate LEDs or may be a mechanical type indicator having differentfirst and second positions, each having an associated color.

An AED incorporating aspects of the invention includes defibrillationcircuitry housed within an enclosure, a first processor programmed toperiodically test the operability of the defibrillation circuitry and asecond processor in communication with the first processor. The AEDfurther includes a visual indicator, as described above, positioned atthe exterior of the enclosure that is operatively connected to thesecond processor. The second processor is programmed to control thevisual indicator in response to the periodic test results provided to itby the first processor. Alternatively, the first and second processorsmay be combined into a single processor.

In one configuration, the second processor is programmed to 1) cause theindicator to continuously present a first color, e.g., green, when thedefibrillator is on and the periodic test result is that thedefibrillation circuitry is operating normally; 2) cause the indicatorto intermittently present the first color when the defibrillator is offand the periodic test result is that the defibrillation circuitry isready to operate normally; 3) cause the indicator to continuouslypresent a second color, e.g., red, when the defibrillator is on and theperiodic test result has detected an error in the defibrillationcircuitry and 4) cause the indicator to intermittently present thesecond color when the defibrillator is off and the periodic test resulthas detected an error in the defibrillation circuitry.

In another aspect, the invention is directed to an AED that providesvisual and/or audible indications of the condition of a defibrillatorduring use. These indications relate to the operation of the AED inconjunction with the electrode pad assembly used to monitor a patient'sheart activity and administer defibrillation shocks.

An AED related to this aspect of the invention includes defibrillationcircuitry housed within an enclosure and an electrode pad assemblyadapted for electrical communication with the defibrillation circuitryat one end and a patient at the other end. The AED further includes aprocessor programmed to monitor the operation of the defibrillationcircuitry and electrode pad assembly and a visual indicator positionedat the exterior of the enclosure and operatively connected to theprocessor. The AED may also include a speaker. The processor isprogrammed to control the visual indicator and/or speaker in response tothe results of the operation monitoring.

These and other aspects and advantages of the invention will becomeapparent from the following detailed description and the accompanyingdrawings which illustrate by way of example the features of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a top sectional view of an AED with a battery packinstalled;

FIG. 1B illustrates a top sectional view of the AED with the batterypack removed;

FIG. 2 illustrates a bottom view of the battery pack;

FIG. 3 illustrates a side sectional view of the AED including thebattery pack;

FIG. 4 illustrates a side sectional view of the battery pack includingfirst and second battery units;

FIG. 5 illustrates a block diagram of one configuration of circuitrycontained within the battery pack and the AED;

FIG. 6 illustrates a block diagram of another configuration of circuitrycontained within the battery pack and the AED; and

FIG. 7 is a perspective view of an AED including an active statusindicator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1A illustrates a top sectional view of the Semi-Automatic ExternalDefibrillator (“AED”) 100 that includes a battery system, for examplebattery pack 110. The AED 100 is a device to treat cardiac arrest thatis capable of recognizing the presence or absence of ventricularfibrillation or rapid ventricular tachycardia or other shockable cardiacarrhythmias, and is capable of determining, without intervention by anoperator, whether defibrillation should be performed. Upon determiningthat defibrillation should be performed, the AED automatically chargesand requests delivery of electrical energy to electrodes that attach toa patient to deliver the energy to the patient's heart.

The battery pack 110 provides power to components such as electronicsand a charger located in the AED 100. The charger charges a capacitor564 (FIG. 5) of the AED 100 that provides the electrical energy to theelectrodes attached to the patient. The AED 100 includes a generallyrectangular shaped battery well 120 that is constructed and arranged tohouse the battery pack 110. The battery pack 110 is sized to slide inand out of the battery well 120 to releasably connect a power supply ofthe battery pack 110 to the AED 100.

FIG. 1B illustrates a top sectional view of the AED 100 and the batterywell 120 with the battery pack 110 removed. An entrance 210 of thebattery well 120 accommodates alignment of the battery pack 110 withinthe battery well 120.

FIG. 2 illustrates a bottom view of the battery pack 110. Referring toFIGS. 1B and 2, an opposite end of the battery well 120 includes awedge-shaped feature 230 that corresponds to a wedge-shaped receptacle235 located in the battery pack 110. When inserting the removablebattery pack 110 to the AED 100, the battery pack 110 is guided along bythe battery well 120 to the wedge-shaped feature 230. The battery pack110 is aligned at the end of its travel by the wedge shaped feature 230in the battery well 120 via the corresponding wedge shaped receptacle235 in the battery pack 110.

Referring to FIG. 1A, to maintain the battery pack 110 in a connectedposition relative to the AED 100, the battery pack 110 includes a latch130 that retains the battery pack 110 within the battery well 120 whenthe battery pack is fully inserted into the battery well 120. An end ofthe latch 130 connects with a spring 132 to bias the latch in a normallyextended position. In the normally extended position, a latching end 134of the latch 130 extends to enter a corresponding slot 136 located inthe AED 100. The latch 130 is moveable in a plane parallel to the spring132 to compress the spring 132 to release the latching end 134 from theslot 136. When the latching end 134 is released from the slot 136, anejection spring 137 located on the AED 100 pushes on the battery pack110 to eject the battery pack 110 from the battery well 120. The batterypack 110 includes a slot 138 from which the latch 130 extends. Even in afully contracted position, the latch 130 extends past the slot 138.

The battery pack 110 also includes a printed circuit board (PCB) 140including exposed electrical terminals 150 to connect the printedcircuit board 140 to electrical circuitry contained in the AED 100, asdescribed in more detail below. The PCB 140 includes electricalcomponents that connect to circuitry of the AED 100 when the batterypack 110 is installed in the AED 100. The battery pack 110 includes awindow 160 that is located proximate to a visual indicator, such aslight emitting diode (LED) 550 (FIG. 5). The window 160 allows anoperator to view the LED 550 when the battery pack 110 is removed fromthe AED 100. Thus, the operator can determine a status of at least oneof the AED 100 and the battery pack 110 independent of the battery pack110 being connected to the AED 100. It should be appreciated that theAED 100 could also include a window located proximate to the batterypack window 160 so that an operator can view the LED 550 when thebattery pack is inserted in the AED 100.

FIG. 3 illustrates a side sectional view of the AED 100 including thebattery pack 110. The electrical terminals 150 of the PCB 140 contact aconnector 310 located within the AED 100, to electrically connect thebattery pack PCB 140 with an AED PCB 320.

FIG. 4 illustrates a side sectional view of the battery pack 110. Thebattery pack 110 includes a first power supply, such as battery unit410. The battery unit 410 powers essential power needs of the AED duringa main operating mode, for example when the AED is powered on. Anessential power need includes, for example, the power necessary tocharge the capacitor 564 to delivery energy to the patient. The batteryunit 410 is preferably not being drained of power when the AED ispowered off.

The battery unit 410 includes one or more battery cells, or other powersupplies, that are electrically connected together. The power supply mayinclude other forms of energy storage, for example based on chemical orkinetic principles, such as a flywheel storage device. The battery cellscan include, for example, ⅔ A size batteries and/or C size batteries.The number of batteries used varies depending on a particularapplication but typically includes five or ten ⅔ A size batteries orfour C size batteries. The five ⅔ A size batteries or four C sizebatteries are connected in series. Also, two sets connected in parallelof five ⅔ A batteries connected in series can be used for the batteryunit 410. The battery unit 410 preferably powers electronics and acharger located in the AED 100.

The battery pack 110 also includes a secondary power supply, such assecondary battery 420. The secondary battery 420 powers at least aportion of at least one of the AED and the battery pack 110 in analternate mode, such as when at least a portion of the AED is poweredoff. Those skilled in the art will appreciate that the secondary battery420 could also be used to power the AED during other modes, such as asleep mode or when the AED is powered on. The secondary battery 420typically includes a single 9 Volt battery, but other power suppliescould be used, such as other sized batteries or other forms of energystorage. In a preferred embodiment, the battery pack 110 accommodatesreplacement of the secondary battery 420. The secondary battery 420 canbe sized smaller than the battery unit 410 and contain energy sufficientto power, for example, electric circuitry of the AED 100 and the batteryPCB 140.

The secondary battery 420 can be used to power circuitry exclusive of astate of the battery unit 410 and without draining power from thebattery unit. Diodes 502 (FIG. 5) electrically isolate the battery unit410 from the secondary battery 420. Electric circuitry of the batterypack PCB 140 is described in more detail below with regard to FIG. 5.Such circuitry includes a socket to removably receive a memory device(FIG. 4), such as a memory card 430 or a multi-media card (MMC).

When the AED 100 is powered on and attached to the patient, the memorycard 430 records the patient's electrocardiogram (ECG) signals, audiosignals received from a microphone located on the AED 100, and otheroperational information such as results of an analysis done on thepatient by software of the AED 100. The memory card 430 may also holdfiles that may be used to upgrade the software of the AED 100 or toprovide user training mode software for the AED.

FIG. 5 shows a block diagram illustrating battery pack circuitry 500contained with the battery pack 110, for example, on the battery packPCB 140, and main unit circuitry 505. The circuitry 500 includes a mainpower switch 510. The main power switch 510 connects with a digitallogic, such as micro-controller 520, that turns the main power switch510 on and off and controls other circuitry 500 of the battery pack PCB140. In addition to or in place of the micro-controller 520, the digitallogic can also include a microprocessor, a programmable logic device(PLD), a gate array and a custom integrated circuit. Other digital logiccould also be used such as a Programmable Interface Controller (PIC)manufactured by Microchip Technologies, located in Chandler, Ariz.

The micro-controller 520 connects with a main AED connector 530 thatconnects circuitry of the battery pack PCB 140 to circuitry of the AED100. When the operator engages a power switch 592 located on the AED100, the micro-controller 520 receives a signal from the main unitconnector 530 indicating that the power switch has been engaged.Thereafter, the micro-controller 520 enables the main power switch 510to provide an electrical power between the battery unit 410 of batterypack 110 and the electronics of the AED 100. The battery pack PCB 140also includes a main battery connector 540 to connect the battery unit410 to the main unit connector 530 and other circuitry of the batterypack PCB 140.

The micro-controller 520 also controls a visual indicator, such as LED550 and an audio indicator, such as sounder 560 that are used toautomatically communicate information to the operator. For example, whenthe AED 100 fails a self-test, the operator is notified by a chirpingsound from the sounder 560. Moreover, the LED 550 blinks green toindicate that a status of components of the AED 100 is within anacceptable operating range. Those skilled in the art can appreciate theopposite could be true, i.e., that a blinking light indicates a faultcondition. According to a preferred embodiment, if the LED 550 is notblinking an error exists, for example, in the circuitry 500, or thebattery unit 410 or secondary battery 420 are depleted. Themicro-controller 520 monitors a signal of a comparator connected tosecondary battery 420 to monitor a status of the secondary battery 420,for example, to determine whether or not power of the secondary battery420 is low or depleted.

Regarding the main unit circuitry 505, a digital signal processor (DSP)562 processes instructions and data of the AED 100. The DSP 562 connectswith a charger circuit 563 and discharger circuit 565 to control thecharging and discharging of main unit capacitor 564. The capacitorcharger 563 connects the battery unit 410 to the capacitor 564. Thecapacitor 564 connects to a discharge circuit 565 that connects topatient interface 566 to deliver shocks to the patient.

The micro-controller 520 also controls an active status indicator (ASI),which in one embodiment is a red and green LED 567 located on the AED100. In an alternate embodiment the ASI may include two separate LEDs, ared LED and a green LED. The micro-controller 520 connects to the redand green LED 567, for example, via pins of the main unit connector 530.The micro-controller 520 causes the LED 567 to blink green when the AED100 is operating properly and causes the LED 567 to blink red whencomponents of the AED are not within the acceptable operating range, forexample, a component of the AED 100 failed during a self-test procedure.If the LED 567 is not blinking when the battery pack 110 is installedinto the AED 100, components of the AED 100 and the battery pack 110should be checked. The operation of the AED self-test procedures and theASI are described further below. The battery pack LED 550 is preferablydisabled when the battery pack 110 is installed.

The secondary battery 420 powers the micro-controller 520, the LED 550and the LED 567, which helps to maintain the integrity of the batteryunit 410 that provides power to electronics and the capacitor chargerlocated in the AED 100. A secondary battery connector 570 connects thesecondary battery 420 to the circuitry of the battery pack PCB 140.

The battery pack circuitry 500 also includes an electrically erasableprogrammable read only memory (EEPROM) 580 connected to themicro-controller 520 and the main unit connector 530. The EEPROM 580stores information that may be relevant to an owner, service person oroperator of the AED 100. The EEPROM 580 stores information regarding,for example, the number of shocks the battery unit 410 has been usedfor, that the AED 100 has been activated, the date of manufacture of thebattery pack 110 and status information regarding a status of componentsof the battery pack 110 and the AED 100. The DSP 562 of the AED 100connects to a bus that connects to a real time clock (RTC) 590, theEEPROM 580 and the micro-controller 520. Typically once per power up ofthe AED 100, the DSP accesses the RTC 590 to set a main unit clock ofthe AED 100 that is located in the DSP.

The main unit circuitry 505 also includes a switch 592, such as anON/OFF switch, that connects to the micro-controller 520 via the mainunit connector 530. A shock switch 594 connects to the DSP 562 to allowan operator to administer a shock to the patient. A speaker 596 andindicator LEDs 598 connect to the DSP 562 to supply instructions orother information to the operator. Front end circuitry 599 connectsbetween the DSP 562 and the patient interface 566 to process and/orprovide the DSP 562 with information from the patient.

With reference to FIG. 6, in another configuration, the AED 10 consistsof a main AED 12 and a removable battery pack 14. The main AED 12includes a PIC processor 16, which is used to control power to the AED,a digital signal processor (DSP) 18, which is the main processor for theAED, and AED circuitry 20, which consists of the remainder of the AEDcircuitry. For a description of additional AED circuitry including thehigh-voltage circuitry used to generate and deliver defibrillationshock, see U.S. Pat. Nos. 5,607,454 and 5,645,571, the disclosures ofwhich are hereby incorporated by reference. Alternate circuitry, withinthe purview of one of ordinary skill in the art, may be developed andemployed. Thus, the scope of this invention is not intended to belimited to the circuitry described in the incorporated references.

The battery pack 14 is similar to that previously described withreference to FIG. 5, except that some components, including themicro-controller 520 (FIG. 5), i.e., the PIC processor, have been movedto the main AED 12 (FIG. 6). The battery pack 14 includes a battery 22,which contains multiple battery cells, a real-time clock 24, which keepstime and can generate an output signal on a regular basis, a powerswitch 26, which is used to couple the battery 22 to the main AED 12,and a 9V battery 20 used to provide power to the PIC processor 16 duringthe times that the power switch 26 is off.

The DSP 18 is configured to run a number of self-tests that check theoperation of the DSP 18 and the AED circuitry 20 on a periodic basis toensure that the AED is fully operational. When the main AED 12 ispowered off, the PIC 16 is placed in a standby mode. The real-time clock24, which is permanently powered from the battery 22, issues a periodicsignal, typically every five seconds. This signal is routed to the PIC16 and causes the PIC to “wake up” from standby mode. At that time, thePIC 16 flashes an ASI 30 to indicate AED status and also decrements acount of the number of times that it has been woken up since the countwas last set. When this count reaches zero, indicating thatapproximately 24 hours have elapsed since the count was last set, thePIC 16 turns the power switch 26 on which applies power to the AEDcausing the DSP 18 to execute startup code.

During the startup sequence, the DSP 18 communicates with the PIC 16 todetermine the reason for the power-up. Typical reasons are that the userpressed the on/off button on the AED or that the PIC 16 has initiated aself-test. If the reason is a self-test, the DSP 18 executes self-testcode which tests a portion or a majority of the AED circuitry 20. Theresults of the self-test are communicated to the PIC 16 which thendisplays the AED status by blinking the ASI 30. The PIC may also beconfigured to sound a sounder, e.g., speaker 32. When the test iscomplete, the DSP 18 sets the wake-up counter to a value which willcause the PIC 16 to wake up the DSP 18 approximately 24 hours later andinitiates main AED 12 shut-down. The PIC 16 then turns off power to themain AED 12 by switching off the power switch 26. In this manner the AEDis tested on a regular basis.

A typical testing schedule is to do the following self-tests at theintervals indicated:

-   -   Every day: basic circuitry tests.    -   Once a week: basic circuitry tests, basic battery tests and        basic high voltage circuit tests,    -   Once a month: basic circuitry tests, additional battery tests        and comprehensive high voltage circuit tests, including a        partial-voltage internal shock.    -   Once every three months: basic circuitry tests, additional        battery tests and comprehensive high voltage circuit tests,        including a full-voltage internal shock.

Tests are performed in a “silent mode” where no user interface elementsare exercised and the user is not able to tell that the tests are beingexecuted. The user may also independently initiate a self-test byholding down the on/off button 42 (FIG. 7) on the AED for five secondswhile turning the unit on. This will cause an extended self-test,similar in scope to the “once ever three months” test, to execute.

With reference to FIG. 7, the ASI 30 is located on the upper right sideof the AED enclosure 34. The status indications provided by the ASI areas follows:

-   -   Steady-on green: the AED is on and operating normally.    -   Blinking green: the AED is off (in the stand-by mode) and is        ready to operate normally.    -   Steady-On red: the AED is on and has detected an error.    -   Blinking red: the AED is off (in the stand-by mode) and the AED        or battery pack needs servicing.    -   Off: battery pack not installed, AED defective, or the 9V        battery is discharged.

Regarding the “blinking red” status, anytime the ASI 30 blinks red, thePIC 16 causes the speaker 32 to beep periodically to call attention tothe AED. The ASI 30 is powered by the replaceable 9V battery 28 in thebattery pack 14. If the 9V battery 28 has discharged, active statusindication will not be available. In this case, the 9V battery 28 shouldbe replaced. Once the 9V battery 28 has been replaced, the ASI 30 willonce again flash a status indication. If the 9V battery 28 is depleted,the AED will still be fully functional and can be used in the on-statenormally.

When the ASI 30 is blinking red, additional indications of the reasonsfor the blinking may be obtained by turning the AED on through theon/off button 42. These additional indications are provided by voiceprompts programmed into the DSP 18 and output over the speaker 32. Thesevoice prompts include:

“Power on self-test failed, error ‘xxx’”—indicates that the AED hasfailed the power-on self-test and is non-operational and needsservicing. The code number xxx indicates the type of problem that theunit is experiencing.

“Battery pack self-test failed, error ‘xxx’”—indicates that the AED'sbattery pack is non-operational and needs servicing. The code number xxxindicates the type of problem that the unit is experiencing.

“Error ‘xxx’, service required”—indicates that the AED has detected aninternal error, is non-operational and needs servicing. The code numberxxx indicates the type of problem that the unit is experiencing.

“Battery pack low”—indicates that the battery pack capacity is low andshould be replaced soon. The AED will still be able to deliver at leasta minimum of six defibrillation shocks the first time this message isspoken.

“Replace battery pack”—indicates that the battery pack is almostdischarged and that the AED may not be able to deliver defibrillationshocks. The battery pack should be immediately replaced.

“Replace 9V battery”—indicates that the 9V battery in the battery packneeds to be replaced. The unit may not provide active status indicationduring standby mode in this condition, but the AED is still fullyfunctional when turned on and may be used to treat patients. The 9Vbattery should be replaced as soon as possible.

As previously indicated with reference to FIG. 5, a speaker 596 andindicator LEDs 598 are connected to the DSP 562 to supply instructionsor other information to the operator. With further reference to FIG. 7,in one configuration of the AED, these indicators 36 are located on thefront panel of the enclosure 34 and include a red “check pads” LED, ared “do not touch patient” LED and a green “analyzing” LED.

As shown in FIG. 6, the indicator LEDs 36 are directly controlled by theDSP 18. Each LED 36 has a separate control line 38 and driver circuit40. When the control line 38 is active the LED 36 is powered and lightsup. The DSP 18 determines when to enable an LED 36 based on systemstate, i.e., connecting, motion, analyzing. The LED 36 can blink undersoftware control by enabling and disabling the control line 38 at timedintervals.

The DSP 18 enables an LED 36 under the following conditions. The “checkpads” LED blinks when the DSP 18 detects that the patient electrodes arenot properly applied. The “do not touch patient” LED blinks when the DSP18 detects patient motion and at times when the operator should stayclear of the patient. The “analyzing” LED blinks when the DSP 18 isanalyzing the patient's ECG Signal. The process of determiningconditions that activate these LEDs is described below within thecontext of additional indications provided by voice prompts.

In addition to the indications provided by the blinking LEDs 36, the DSP18 is programmed to output voice prompts over the speaker 32 inassociation with certain conditions. Voice prompts associated with the“check pads” LED include “connect pads” and “check pads”. “Connect pads”indicates that the DSP 18 has determined that the pads are not properlyconnected to the unit or not placed on the patient. This determinationmay be made by measuring the impedance across the pads. A high impedanceis an indication that the pads are either not connected to the unit ornot placed on the patient while a low impedance serves as an indicationthat the pads may be shorted together. What is considered “high” or“low” impedance is dependent on the electrical characteristics ofelectrode pad assembly and the internal defibrillator circuitry. “Checkpads” indicates that the pads are making improper contact with thepatient and that the impedance is out of range, i.e., either too high ortoo low, for proper ECG analysis and shock delivery.

Voice prompts associated with the “do not touch patient” LED include “donot touch patient”, “stop motion” and “stop interference”. “Do not touchpatient” indicates that the DSP 18 is in the process of analyzing thepatient's heart rhythm and that the operator should not touch thepatient. The DSP 18 is programmed to analyze ECG signals once it hasdetermined that the electrode pads are making good connection to thepatient. The “do not touch patient” message is spoken at the beginningof the ECG analysis period and also if motion or interference has beendetected. “Stop motion” indicates that the DSP 18 has detected motion inthe patient, such as may occur during the administering of CPR. “Stopinterference” indicates that the DSP 18 has detected interference on theECG signal. In each of these cases, the DSP 18 monitors thecharacteristics of the ECG signals for indications of patient motion,e.g., an unexpected spike in the signal, and signal interference, e.g.,a signal pattern containing noise or a signal of weak amplitude.

Voice prompts associated with the “analyzing” LED include “analyzingheart rhythm” and “analyzing interrupted”. “Analyzing heart rhythm”indicates that the DSP 18 is actively analyzing the patient's ECGsignal. The DSP 18 will continue analyzing until it has determinedwhether a rhythm is shockable or non-shockable or analyzing isinterrupted for some reason. “Analyzing interrupted” indicates that theDSP 18 has determined that accurate ECG analysis is not possible and hasceased analyzing. The DSP 18 determines this condition by monitoring theECG signal as previously described with respect to patient motion,signal interference and check pads. While the other LEDs may blinkduring this process, the “analyzing” LED will not be lit during thismessage.

While the invention has been described above by reference to variousembodiments, it will be understood that many changes and modificationscan be made without departing from the scope of the invention. It istherefore intended that the foregoing detailed description be understoodas an illustration of the presently preferred embodiments of theinvention, and not as a definition of the invention. It is only thefollowing claims, including all equivalents, which are intended todefine the scope of this invention.

1. An external defibrillator, comprising: a battery; defibrillationcircuitry housed within an enclosure having an exterior, thedefibrillation circuitry powered by the battery including a computerhaving programming to initiate and run recurring self-tests, whichinclude at least some portion of the defibrillation circuitry and toperform a rescue, the self-tests occurring at intervals and capable ofdetermining an operational status of the external defibrillator, aswitch for a user to switch the external defibrillator from OFF to ON,wherein ON activates the defibrillation circuitry and its associatedprogramming to perform a rescue, and OFF does not activate thedefibrillation circuitry and its associated programming to perform arescue but allows self tests to be conducted; an active status indicatorcomprising a light source that illuminates, the light source operated bythe programming running on the computer, wherein the light source has afirst illumination continually to indicate to an observer that theexternal defibrillator is OFF and that the most recent self-test hasdetermined that the operational status is normal and thus the externaldefibrillator is ready to operate normally when turned ON and thatpresently maintenance is not required.
 2. The defibrillator of claim 1wherein the programming causes the active status indicator to present asecond illumination in place of the first illumination when thedefibrillator is ON and a self-test conducted as part of the rescuedetermines that the defibrillation circuitry is operational to indicateto the observer that the defibrillation circuitry is operating normally.3. The defibrillator of claim 1 wherein the programming causes theactive status indicator to present a third illumination in place of thefirst illumination when the defibrillator is ON and a self-testconducted as part of the rescue sequence determines that maintenance isrequired to indicate to the observer that maintenance is required. 4.The defibrillator of claim 1 wherein the programming causes the activestatus indicator to present a fourth illumination in place of the firstillumination when the defibrillator is OFF and the most recent self-testhas indicated that maintenance is required to indicate to the observerthat maintenance is required.
 5. The defibrillator of claim 1 whereinthe first illumination includes blinking.
 6. An external defibrillator,comprising: a battery pack; defibrillation circuitry housed within anenclosure having an exterior and connected to the battery pack, thedefibrillation circuitry including a computer operating programmingwherein the programming includes recurring self-tests of thedefibrillation circuitry, the self-tests occurring at intervals, aswitch for switching the external defibrillator from OFF to ON, thedefibrillation circuitry when OFF being incapable of delivering a shockto a patient but able to perform recurring self-tests, and an activestatus indicator comprising a light source that illuminates, the lightsource operated by the programming running on the computer, wherein thelight source is illuminated continually indicating that the externaldefibrillator is OFF and that the most recent self-test has determinedthat the external defibrillator is ready to operate normally if switchedON.
 7. The external defibrillator of claim 6 wherein the defibrillationcircuitry and electrode pads comprise electrical circuitry defining ahigh impedance threshold and a low impedance threshold and wherein aprocessor measures the impedance across the electrode pads, measures theimpedance to the high impedance threshold and the low impedancethreshold, and activates a second indicator when the measured impedanceis either below the low impedance threshold or above the high impedancethreshold.
 8. The external defibrillator of claim 7 wherein activestatus indicator comprises a LED and the processor activates the LED bycausing the LED to blink.
 9. The external defibrillator of claim 8wherein active status indicator further comprises a visual messagedisplay related to the operation being monitored.
 10. The externaldefibrillator of claim 9 wherein the visual message display relates to adirection to check the electrode pads.
 11. The external defibrillator ofclaim 7 further comprising a speaker, wherein the processor is furtherprogrammed to output an auditory message through the speaker related tothe operation being monitored.
 12. The external defibrillator of claim11 wherein the auditory message relates to a direction to connect theelectrode pads.
 13. The external defibrillator of claim 6 wherein thedefibrillation circuitry and electrode pads comprise electricalcircuitry defining an impedance range proper for ECG analysis and shockdelivery and wherein a processor is programmed to measure the impedanceacross the electrode pads, compare the impedance to the impedance range,and activate a second indicator when the measured impedance is outsidethe impedance range.
 14. The external defibrillator of claim 13 whereinthe active status indicator comprises a LED and the processor activatesthe LED by causing the LED to blink.
 15. The external defibrillator ofclaim 14 wherein the active status indicator further comprises a visualmessage display related to the operation being monitored.
 16. Theexternal defibrillator of claim 15 wherein the visual message displayrelates to a direction to check the electrode pads.
 17. The externaldefibrillator of claim 13 further comprising a speaker, wherein theprocessor is further programmed to output an auditory message throughthe speaker related to the operation being monitored.
 18. The externaldefibrillator of claim 17 wherein the auditory message relates to adirection to check the electrode pads.
 19. The external defibrillator ofclaim 6 wherein a processor is programmed to analyze ECG signals basedon electrical signals received through the electrode pads; monitor theECG signals for spikes, noise, and weak amplitude; and activate theactive status indicator under any one of the following conditions: ECGsignals being analyzed, spike detected, or noise or weak amplitudedetected.
 20. The external defibrillator of claim 19 wherein the activestatus indicator comprises a LED and the processor activates the LED bycausing the LED to blink.
 21. The external defibrillator of claim 20wherein the active status indicator further comprises a visual messagedisplay related to the operation being monitored.
 22. The externaldefibrillator of claim 21 wherein the visual message display relates toa direction to not to touch the patient.
 23. The external defibrillatorof claim 19 further comprising a speaker, wherein the processor isfurther programmed to output an auditory message through the speakerrelated to the condition.
 24. The external defibrillator of claim 23wherein the condition comprises ECG signals being analyzed and theauditory message relates to a direction to not to touch the patient. 25.The external defibrillator of claim 23 wherein the condition comprises aspike detected and the auditory message relates to a direction to stopmotion.
 26. The external defibrillator of claim 23 wherein the conditioncomprises noise or weak amplitude detected and the auditory messagerelates to a direction to stop interference.
 27. The externaldefibrillator of claim 6 wherein a processor is programmed to analyzeECG signals based on electrical signals received through electrode padsand to activate the active status indicator during signal analysis. 28.The external defibrillator of claim 27 wherein the active statusindicator comprises a LED and the processor activates the LED by causingthe LED to blink.
 29. The external defibrillator of claim 28 wherein theactive status indicator further comprises a visual message displayrelated to the operation being monitored.
 30. The external defibrillatorof claim 29 wherein the visual message display relates to analyzingheart rhythm.
 31. The external defibrillator of claim 27 furthercomprising a speaker, wherein: the defibrillation circuitry and theelectrode pads comprise electrical circuitry defining an impedance rangeproper for ECG analysis and shock delivery, and the processor isprogrammed to: output a first auditory message through the speaker whenECG signals are being analyzed; measure the impedance across theelectrode pads, compare the impedance to the impedance range, and outputa second auditory message through the speaker when the measuredimpedance is outside the impedance range; and monitor the ECG signalsfor spikes, noise, and weak amplitude and output a third auditorymessage through the speaker under either of the following conditions:spike detected or noise or weak amplitude detected.
 32. The externaldefibrillator of claim 31 wherein the first auditory message relates tothe act of analyzing heart rhythm.
 33. The external defibrillator ofclaim 31 wherein the second and third auditory messages relate to theinterruption of heart rhythm analysis.